var olnav = document.querySelector('.ol-nav')
var as = document.querySelectorAll('.ol-nav a')
olnav.onclick = function(e) {
    if (e.target.localName == "a") {
        index = e.target.dataset.a
    }
    for (var i = 0; i < as.length; i++) {
        as[i].classList.remove('active')
    }
    as[index].classList.add('active')
}